Microelectromechanical systems (MEMS) technology is used to integrate mechanical elements, sensors, actuators, and electronics on a common silicon substrate through microfabrication technology. MEMS devices include pressure sensors, accelerometers, gyroscopes, microphones, digital mirror displays, micro fluidic devices, and so forth. MEMS pressure sensor devices, for example, can be used in a wide range of applications, including commercial applications such as air conditioning, fluid level sensing and flow control.
Depending on the nature of the application, different types of pressure sensors are commonly used. Exemplary pressure sensors include absolute pressure sensors and differential pressure sensors. An absolute pressure sensor is a sensor that has an output related to the absolute pressure of an external environment with respect to a known, constant pressure (typically vacuum). A differential pressure sensor, on the other hand, is a sensor whose output is related to a difference in pressures between two regions, and typically includes a semiconductor membrane separating two ports coupled to two different pressure levels. A gauge pressure sensor is generally a differential pressure sensor in which the sensor has an output related to the pressure relative to atmospheric pressure.
Differential pressure sensors may advantageously be used with differential circuits to provide higher linearity and greater noise immunity than the single-ended circuits typically used with absolute pressure sensors. However, there are significant challenges to be surmounted in the packaging of MEMS differential pressure sensors due at least in part to the necessity for the pressure sensors to interact with the outside environment, the fragility of many types of pressure sensors, severe size and cost constraints, and so forth. Indeed, many pressure sensor applications require smaller size and low cost packaging to meet aggressive cost targets. Additionally, pressure sensor applications require configurations that are largely impervious to package stress, which can otherwise cause instability of the pressure sensor and output shifts in the pressure sensor.
Additionally, one or both sides of a differential pressure sensor might be in close proximity to water or other corrosive chemicals. To protect against the corrosive environment, pressure sensors are provided with various coatings, encapsulants, or diaphragms made from various elastic gels, polymers, or other materials. However, these protection schemes can further add to the complexity of manufacturing such sensors, resulting in increased cost, reduced reliability, and/or reduced ability to measure the pressure (e.g., due to the presence of a thick coating on the sensing diaphragm).